The hearing for Holmes, who is charged with 166 counts of murder, attempted murder and weapons charges for the July 20 shooting that killed 12 people and injured 58 others, is being held in Centennial, Colo., The Denver Post reported.

Holmes has yet to enter a plea.

The video from the shooting scene showed employees at the Century 16 movie theater in Aurora drop to the floor and dozens of people rushing to exit the theater.

It also showed Holmes walking into the theater, wearing a long-sleeved shirt, dark pants and a dark beanie stocking cap.

"He was very relaxed," Oviatt said in court. "It was like there weren't normal emotional responses to anything. He seemed very detached."

The hearing, expected to last a week, is to determine if sufficient evidence is available to move the case against Holmes to trial, The New York Times reported.

Prosecutors are laying out their case for the first time, the Post said.

Police reports from the day of the shooting noted Holmes "stared off in space" and "seemed out of it" at his arrest. Oviatt said in court Holmes understood directions and fully complied with officers, "not doing anything, not in any hurry, not excited, not urgent about anything."

Oviatt also said Holmes warned him of explosives in his apartment, wired to go off if they were tripped.

Officers who entered the theater and drove victims to local hospitals also testified Monday, the Post reported.

Officer Aaron Blue spoke about holding victim Jessica Ghawi in the back of his car as another officer drove them, saying, "Every time she moved, she stopped breathing," and Grizzle held back tears as he described entering the crime scene and seeing "several bodies throughout the theater laying motionless" and later driving six victims to hospitals.

Two overflow rooms were set up with a live video feed of the proceedings. One room was to be reserved for 100 or so victims and family members who said they planned to attend.

Chief Judge William Sylvester is responsible for determining if there is "probable cause" to believe a crime was committed.

While prosecutors must show enough evidence exists to proceed to trial, defense attorneys may call their own witnesses to contradict prosecution witnesses, especially on Holmes' "mental state," Sylvester ruled last week.

If Holmes is found legally insane or to have a mental defect, the death penalty is off the table, former Denver District Attorney Craig Silverman told the Los Angeles Times.

Holmes' attorneys have suggested in court their client, who dropped out of the University of Colorado-Denver's neuroscience doctoral program after failing an oral exam in June, suffers from mental illness.

Prosecutors have called Holmes a promising doctoral candidate who violently unraveled and methodically prepared for the movie theater attack for months.

Assistant District Attorney Karen Pearson has said in court Holmes told a classmate as early as March he wanted to kill people.

On June 7, the day he failed a key oral exam at school, he bought a lightweight AR-15 semiautomatic rifle to add to his collection, prosecutors have said.

That collection included combat gear, explosive materials and thousands of rounds of ammunition, prosecutors have said.

When he was arrested minutes after the shooting, Holmes was dressed entirely in black body armor, much like the SWAT team of police that responded.

The shooting was among the worst mass shootings in U.S. history, although it has been overshadowed by later attacks, including last month's Newtown, Conn., massacre of 20 Sandy Hook Elementary School students and six school employees.

On Saturday, 4 miles from the Aurora mall where the movie theater shooting occurred, four people were killed, including the suspected gunman, after a 6-hour standoff at a townhouse.

United Press International is a leading provider of news, photos and information to millions of readers around the globe via UPI.com and its licensing services.

With a history of reliable reporting dating back to 1907, today's UPI is a credible source for the most important stories of the day, continually updated - a one-stop site for U.S. and world news, as well as entertainment, trends, science, health and stunning photography. UPI also provides insightful reports on key topics of geopolitical importance, including energy and security.

A Spanish version of the site reaches millions of readers in Latin America and beyond.

UPI was founded in 1907 by E.W. Scripps as the United Press (UP). It became known as UPI after a merger with the International News Service in 1958, which was founded in 1909 by William Randolph Hearst. Today, UPI is owned by News World Communications.